As high-end computers increase in complexity and chip count, the interconnections between IC chips have grown and bottleneck delays for these interconnections have increased. There have been many efforts to address the bottleneck delays by conveying some of the signals between chips by optical means. In these attempts, bottlenecked electrical signals are converted to optical signals by light transmitters, the optical signals are then propagated over long distances across an interconnect board by way of optical waveguides formed therein, and then received by light receivers and converted back to electrical signals. The optical waveguides in these boards are typically formed by polymer layers built up on top of the base substrates of the boards. However, the polymer materials for these layers have anisotropic dielectric constants, and thus have high degrees of birefringence. The birefringence hinders the transmission of signals in the waveguides by causing spatial and temporal dispersion of optical signals, and therefore hinders the ability to provide long interconnects.
The buildup process used to construct the waveguide layers is relatively expensive because a number of steps are involved, including steps to form cladding layers, core layers, and reflecting mirrors. The reflecting mirrors are used to direct light signals into and out of the waveguides from the top surface of the interconnect board, where the light transmitters and light receivers are located. Many such steps are involved when several tiers of waveguides are formed over one another. The number of steps involved increases the chances of a defect occurring in the manufacturing process, which decreases the yield of the process and increases the manufacturing cost.
Thus, in order to successfully pursue optical interconnects for electrical systems, the birefringence and dispersion of the optical signals conveyed through the waveguides must be reduced, the manufacturing yield must be increased, and the manufacturing costs must be reduced.